The fascination of guessing the sex of the unborn baby in the womb is deeply ingrained in all cultures. Various folklore techniques have been used. They have ranged from torque on suspended wedding rings to color reflections from flowers, coins held near the belly or colors transmitted through various unguents applied to the belly. The shape of the belly was also a sure indicator--round could be either a boy or a girl depending on the specific culture. Needless to say, the prognosticators were either right or wrong--usually about half the time. None of the methods were scientifically based.
Recently some methods based on science have had favor based to some degree upon endocrinology. Acne-like complexion changes in the mother have been held to indicate a probable girl. These are based upon supposed excesses of female hormones. Improvement in the mother's complexion was suggestive of a probable boy. The reasoning was a supposed neutralization of any excessive female hormones by the male hormones from the boy fetus.
There may be some basis to this method as statistically, some doctors who have followed up their original predictions claim improved guessing averages. However, recent improvements in hormone assays in the blood of pregnant women have not shown any significant alteration in specific hormone levels between women carrying boys and women carrying girls.
Sure methods exist for determining the sex of the fetus, but they are invasive of the womb or fetus to some degree. Amniocentesis involves insertion of a cannula or needle into the amniotic sac. In the hands of a skilled practitioner who follows the fetal position with various visualization aids, there is little danger, but such dangers do exist either from contact between the fetus and the sampling needle or from the action upon the fetus of the ultrasound or x-ray visualization aids.
Another direct method involves visualization of the genitalia by following the fetus with ultra-sound wands until the fetus and the transducer are properly positioned to provide an image of the fetal genitalia on the ultra-sound monitor. The effect of subjecting the fetus to ultra-sound is controversial.